Valves are often used to control fluid flow through a fluid system, for example, by shutting off, regulating, or redirecting flow applied to an inlet fluid passage of the valve. In many valves, a valve element is selectively movable to block, meter, divert, or otherwise control fluid flow, for example, to another passage of the valve, such as an outlet passage. Such a valve element may be placed in sealing engagement with one or more valve seat members, to limit or prevent leakage of system fluid past the valve element. Valve elements may be movable in a variety of different ways with respect to the seat member, including, for example, axial movement of the valve element towards and away from the seat member, sliding movement through the seat member, or rotational movement with respect to the seat member. As one example, a rotatable valve element may be provided with a through passage, such that when the valve element is rotated to align the through passage with an inlet passage of the valve, flow of fluid through the valve seat and the valve element passage (for example, to a second, outlet valve passage) is permitted. When the rotatable valve element is rotated to move the through passage out of alignment with the valve inlet passage (i.e., a valve closed position), fluid flow is blocked, and the valve seat provides sealing engagement with the valve element to reduce or prevent leakage past the valve element. One example of such a valve is a ball valve, provided with a spherical outer surface against which a complementary shaped spherical surface of the valve seat is configured to seal.
One such ball valve is described in U.S. Pat. No. 4,113,229 (the “'229 patent”), the disclosure of which is incorporated herein by reference in its entirety. In the valve described in the '229 patent, a spring member biases a valve seat towards sealing engagement with a valve element or ball, to provide a seal between the ball and seat member at lower pressures. In response to fluid pressure, the seat member axially moves or “floats” within the valve body. By exposing the upstream system fluid to outward facing seat member surfaces having a surface area that exceeds the surface area of inward facing seat member surfaces, the fluid pressure acts against a net effective area to force or urge the valve seat into tighter sealing engagement with the ball.
However, it may be desirable to limit these fluid pressure sealing forces applied to the floating seat member by the pressurized system fluid, for example, to reduce seat wear or to reduce the operating force required to operate the valve element. In one embodiment, the sealing forces may be limited by reducing the net effective area upon which the upstream fluid pressure may act. As one example, an axially movable seat member may include a seat carrier having a reduced diameter outer or tail portion to which the upstream or inlet system pressure is exposed, such that the net effective area (the amount by which the outward facing pressurized surfaces exceed the inward facing pressurized surfaces) is limited or reduced, thus limiting the upstream pressure sealing forces applied to the seat. One way of reducing this net effective area is by isolating the spring member, and the outward facing surface against which the spring member acts, from the upstream fluid pressure. An example of such a valve arrangement is described in U.S. Pat. No. 4,572,239 (the “'239 patent”), the disclosure of which is incorporated herein by reference in its entirety.
As shown in FIG. 1, the valve of the '239 patent includes live-loaded members or spring members (disc springs 110′, 112′, 114′) that bias the valve seat (seat carrier C′ with seat ring 120′) towards sealing engagement with a trunnion-style valve element (closure member B′) disposed in a central passageway 20′ of the valve body A′. The disc springs 110′, 112′, 114′ are in a valve cavity sealed from inlet system fluid pressure (applied to end fitting D′) by an o-ring seal 100′ that provides a seal between the seat carrier C′ and the inlet passage (of end fitting D′). As such, the fluid pressure sealing force is limited to the surface area difference between the outward facing surfaces of the seat carrier C′ tail portion and the o-ring seal 100′, and the inward facing surfaces of the seat carrier that are radially inward of the sealing portion of the seat ring 120′. As described in greater detail in the '239 patent, by positioning the seat ring sealing portion radially inward of the seal chamber surface (or outer diameter of the o-ring 100′), the net effective area ensures an inward urging of the seat carrier C′ due to upstream system pressures. This inward urging is transmitted through the o-ring 100′, as upstream fluid pressure forces the o-ring seal 100′, backup ring 104′, and gland 106′ against disc springs 110′, 112′, 114′, thereby forcing the disc springs and seat carrier C′ towards sealing engagement with the closure member B′. As a result, a system pressure-assisted sealing force is applied in series with the live-loaded sealing force of the disc springs 110′, 112′, 114′.
FIG. 1A graphically illustrates upstream sealing load between a valve seat and a valve element (e.g., a ball) as a function of differential system pressure in a valve in which a fluid-driven sealing force is in series with a spring-loaded or live-loaded sealing force. Line 1a indicates sealing load provided by the system pressure, and line 2a identifies additional sealing load (represented by the displacement between lines 1a and 2a) provided by the live-loaded sealing force (e.g., by one or more spring members). As shown, at lower system pressures, sealing load is predominantly provided by the live-loaded sealing force. However, as the system pressure increases, the resulting fluid-driven sealing force predominates the total sealing load (e.g., as live-loaded spring members are further compressed and exert a reactive load against the fluid driven sealing force). When the system pressure exceeds an amount sufficient to fully compress the source of the live-loaded sealing force (at the intersection of lines 1a and 2a), sealing load is exclusively provided by the fluid-driven system pressure.
As further described in the '239 patent, to provide suitable sealing forces between the seat ring 120′ and the closure member B′ against downstream system pressures, the sealing portion of the seat ring 120′ is also configured to have an outside diameter that is greater than the outside diameter of the carrier tail portion 62′ (or the inside diameter of the o-ring seal 100′ surrounding the tail portion), such that the net effective area which provides the net force of downstream fluid pressure acting on the seat ring 120′ comprises the annulus defined between the outer diameter of sealing contact by the downstream seat ring engaging surface with the ball portion and the outer diameter of the associated carrier tail portion 62′. As a result, the fluid pressure within the valve cavity provides a system pressure assisted sealing force on the downstream seat toward sealing engagement with the valve element. This sealing force is applied in parallel with the downstream disc springs 110′, 112′, 114′.
FIG. 1B graphically illustrates upstream sealing load between a valve seat and a valve element (e.g., a ported ball or plug) as a function of differential system pressure in a valve in which a fluid-driven sealing force is applied in parallel with a spring-loaded or live-loaded sealing force. Line 1b indicates sealing load provided by the system pressure, and line 2b identifies additional sealing load (represented by the displacement between lines 1b and 2b) provided by the live-loaded sealing force (e.g., by one or more spring members). As shown, at lower system pressures, sealing load is predominantly provided by the live-loaded sealing force. However, unlike the sealing load performance illustrated in FIG. 1A, as the system pressure increases, the live-loaded sealing force remains relatively constant, thereby providing an increased sealing load (as compared to the sealing load performance illustrated in FIG. 1A), particularly at higher system pressures.